This invention generally relates to the testing of integrated circuits (xe2x80x9cICxe2x80x9d) including a method for removing and an apparatus that removes ICs or chips from a substrate after the chip has been tested on the substrate. More particularly, this invention relates to temporary chip attach (xe2x80x9cTCAxe2x80x9d) technologies in which chips are mounted to a substrate carrier for functional performance testing through the substrate and then the removal of those chips from the substrate for further use if the chip passes the functional testing. In certain embodiments, the present inventive methods and apparatus can remove the chip from the substrate without physical or mechanical contact of a shearing device or clamp with the chip thereby reducing damage that may be caused to the chip during or after the functional performance testing. In other embodiments, the present inventive methods and apparatus remove the chip from the substrate through use of a computer controlled servomotor to precisely regulate the shearing forces used to remove the chip.
The demand for additional intricacy of integrated circuits has imposed an increase in the design complexity of IC. Indeed, ICs today are often manufactured in stages having multiple levels of circuitry and electronic components. As the intricacy and complexity of ICs increase, the need to test the IC to ensure functional performance prior to final installation has become more significant and critical. Indeed, there is a critical demand to be able to test and assess electronic components prior to final use.
To satisfy this need for the testing of ICs, temporary chip attach (xe2x80x9cTCAxe2x80x9d) technologies have been developed in which ICs or chips are attached to a temporary substrate carrier for testing of the IC prior to final installation on the final substrate. The typical TCA mechanism uses solder connection points or solder bumps on the chip, known as C4s (controlled collapsed chip connector), to attach the chip to the substrate. With the chip attached to the substrate, it may then be run through functional performance testing while attached to the substrate. Following the testing, the chip may be removed from the substrate for future use. Because the substrate carrier has reduced pad diameters to which the solder bumps attach, when the chip is removed from the substrate, the C4s remain on the chip and may be reused to attach the chip to the final substrate. The technology of testing and removing a chip from a substrate is generally referred to as xe2x80x9cknown good diexe2x80x9d removal.
Various methods and devices have been developed to remove a chip from a substrate. The methods and devices generally can be characterized as a xe2x80x9ccold chipxe2x80x9d or xe2x80x9ccold shear,xe2x80x9d xe2x80x9cwarm shear,xe2x80x9d or a xe2x80x9chot vacuumxe2x80x9d or xe2x80x9chot vacxe2x80x9d removal process. The cold shear devices remove the chip from the substrate by applying shear forces to the chip and substrate with the components being at room temperature. The warm shear devices similarly remove the chip by applying shear forces to the chip and substrate, but the temperature of the components, including the C4s are raised above room temperature. Finally, the hot vac removal methods may or may not use shear forces to remove the chip, but in either method, the temperature of the components is raised to soften the C4s. In the hot vac removal methods, the temperature of the C4s is raised a reflow state. In most known methods of cold and warm shear removal, the devices use preloaded springs or other forces to shear the chip away from the substrate.
One significant problem with the cold and warm shear removal devices is that such systems require that the substrate and/or the chip be physically clamped, or as noted with the use of preloaded springs, the substrate and chip are mechanically separated from each other. The clamping of the chip or substrate, and the mechanical contact of shear devices with the chip and substrate often causes damage to these components. Such damage can destroy the chip. Even if the clamping or contact with the shear device does not damage the chip, due to the spring action, once the chip separates from the substrate, it may be thrown against adjacent components on the substrate, which again could cause damage to the chip or to the adjacent component. While a cushioning tape may be applied to the adjacent components to protect the chip and components, such a solution is very time consuming for the operator and does not reliably prevent damage to the chip or other components attached to the substrate.
Three examples of current devices for removing electronic devices or components from substrates are U.S. Pat. Nos. 5,779,133 and 5,553,766, both by Jackson et al. disclosing an In-Situ Device Removal For Multichip Modules, and U.S. Pat. No. 5,605,277 by Jackson et al. teaching a Hot Vacuum Device Removal Process and Apparatus. The ""133 and ""766 Jackson et al. patents and the ""277 Jackson et al. patent are all assigned to the Applicant.
The ""133 and ""766 Jackson et al. patents generally teach an apparatus that can remove a semiconductor chip forma substrate using a chip lifting assembly that comprises means for gripping the chip, means for applying a lifting force after the chip has reached a temperature where the solder is softened. The lifting force means includes a disk shaped element that is deformable at the same temperatures where the solder is softened. The object of the ""133 and ""766 Jackson et al. patents is to repeatably remove chips from a substrate using reduced temperatures and forces, as compared to other hot shear or cold shear removal methods. By reducing forces required to separate the chip from the substrate, potential damage to the chip is similarly reduced. Both of the apparatuses described in the 3 133 and ""766 Jackson et al. patents specifically require a xe2x80x9cchip gripping meansxe2x80x9d to remove or pry the chip from the substrate.
The ""277 Jackson et al. patent discloses a warm shear method of removing electronic components from substrates in a nondestructive action. The method uses a box oven and vacuum system such that after the temperature of the components and solder is raised to a molten condition, a vacuum is applied to the electronic component to lift it away from the substrate. While the ""277 Jackson et al. method and device described does not appear to use a clamp to hold or remove the electronic component, the method and device do specifically require a physical fixture, including in one embodiment, stainless steel springs, to secure and restrain the substrate when the vacuum is applied to remove the electronic component.
Similar to the Jackson et al. patents, U.S. Pat. Nos. 5,738,267; 5,707,000 and 5,636,781, all by Olson et al., each disclose an Apparatus And Method For Removing Known Good Die Using Hot Shear Process. In the ""267; ""000; and ""781 patents, the apparatuses taught each use a removing means that is secured to the chip to be removed from the substrate, such that after the C4 points reach their reflow temperature, the removing means pulls the chip away from the substrate or device carrier. As described by Olson et al., the chip removal means is secured to or grasps the outer edges of the chip and applies a force or pull directly to the chip to separate it from the substrate. Upon raising the temperature of the solder connection points, the weight or pull of the chip removal means separates the chip from the substrate. As noted for the Jackson et al. methods and apparatuses, the three Olson et al. devices all require a mechanical clamping or grasping of the chip or substrate as part of the elements to remove the chip from the substrate. The forces imparted by the mechanical clamps or other removal means, being essentially uncontrolled, may damage the chip or substrate.
An example of a cold shear chip removal device is provided in U.S. Pat. No. 4,979,287 by Schwab et al., for a Tool For Semiconductor Chip Removal. The ""287 patent discloses a device having several moveable members that respectively apply a bearing force to the chip to be removed and an exteriorly accessible surface of the chip carrier or substrate. By applying opposite forces to the chip and substrate as the moveable members are separated the chip is pried away from the substrate.
An alternative method of removing an IC from a substrate or carrier is taught by Wang in U.S Pat. No. 5,782,403 for an Ultrasonic Chip Removal Method and Apparatus. The disclosed method and apparatus uses lateral (side-to-side) ultrasonic vibration applied to the chip to remove the chip from the substrate. While the temperature of the solder connection points is not increased in the ""403 device, the described embodiments all require that a xe2x80x9cstud elementxe2x80x9d be affixed to the chip for imparting the ultrasonic vibration used to break the solder connections and thereby allow release of the chip. The ""403 device also requires a xe2x80x9csubstrate holderxe2x80x9d to securely lock the substrate to the device.
None of these methods and devices teach a way of removing an IC or chip from a substrate without using some form of a mechanical force applied to the chip or using a mechanical clamp element on the chip or substrate. In view of the need for and use of mechanical contact elements in all of the noted methods, they are all susceptible to the noted problem of causing damage to either the IC and/or the substrate during the process of removing the chip from the substrate.
Accordingly, there remains a need for a method and device to reliably, repeatedly and cost efficiently remove an IC from a substrate without the need for mechanical clamping or grasping elements which may cause damage to either the IC or the substrate. While some force is obviously required to remove the chip from the substrate, the preferred method and device should remove the IC from the substrate without the use of mechanical grasping or clamping, and alternatively if mechanical contact or forces are used, such forces should be accurately controlled to ensure that the minimum required force to remove the IC is used and that the IC and substrate are not damaged as a result of the removal process.
To overcome the shortcomings of the prior art, it is an object of the present invention to provide a method for and an apparatus that can remove an IC from a substrate to which the IC is attached by multiple solder connection points without causing damage to either the IC or the substrate.
To achieve this and other objects, and in view of its purposes, the present invention provides a method for removing an integrated circuit from a substrate, where the integrated circuit is attached to the substrate by a plurality of solder connection points, the method comprising the steps of (a) placing the substrate with the integrated circuit attached thereto in a carrier; (b) placing the carrier with the substrate with attached integrated circuit on a heating plate; (c) pulling the integrated circuit away from the substrate using fluidics after the solder connection points have reached reflow temperature; (d) removing the integrated circuit to a cooling plate; (e) removing the substrate from the heating plate; (f) placing another substrate with the integrated circuit attached thereto in a carrier; and (g) placing the carrier with the substrate and attached integrated circuit on the heating plate for removal of the integrated circuit from the substrate.
It is a further object of the present invention to provide a method for removing an integrated circuit from a substrate, where the integrated circuit is attached to the substrate by a plurality of solder connection points, the method comprising the steps of (a) placing the substrate with the integrated circuit attached thereto in a carrier; (b) placing the carrier with the substrate and integrated circuit attached thereto on a heating plate; (c) forcing the carrier with the substrate and attached integrated circuit to contact a shear element by a programmable motor after the solder connection points have been heated, thereby controllably separating the integrated circuit from the substrate; and (d) capturing the integrated circuit using fluidics as said integrated circuit separates from the substrate.
A further aspect of the present invention, is an apparatus for removing an integrated circuit from a substrate where the integrated circuit is attached to the substrate by a plurality of solder connection points, comprising a pallet having a cavity into which the substrate and integrated circuit fit, the pallet having a plurality of air channels formed in said pallet; a heating plate, onto which the pallet, substrate and integrated circuit are placed to increase the temperature of the plurality of solder connection points to a reflow temperature; and fluidic pulling means applied to the integrated circuit through the pallet plurality of air channels to remove the integrated circuit from the substrate after the plurality of solder connection points achieve a reflow temperature, the fluidic pulling means also maintaining the integrated circuit in the pallet cavity.
Another preferred embodiment of the present invention, is an apparatus for removing an integrated circuit from a substrate where the integrated circuit is attached to the substrate by a plurality of solder connection points, comprising a pallet having a cavity into which the substrate and integrated circuit fit, the pallet having a plurality of air channels formed in the pallet; a shear blade formed in the pallet restricting movement of the integrated circuit; a heating plate, onto which the pallet, substrate and integrated circuit are placed to increase the temperature of the plurality of solder connection points; a shear block restricting the movement of the substrate; a servo motor for moving the pallet, substrate and integrated circuit such that the substrate contacts the shear block after the plurality of solder connection points have been heated, thereby restricting movement of the substrate, the servo motor continuing to move the pallet and shear blade such that the shear blade contacts the integrated circuit and separates the integrated circuit from the substrate; and fluidic pulling means applied through the pallet plurality of air channels to capture the integrated circuit after the integrated circuit separates from the substrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are not intended to be or should be considered restrictive of the invention.